Action Pack – On rails from request to response

Action Pack splits the response to a web request into a controller part (performing the logic) and a view part (rendering a template). This two-step approach is known as an action, which will normally create, read, update, or delete (CRUD for short) some sort of model part (often backed by a database) before choosing either to render a template or redirecting to another action.

Action Pack implements these actions as public methods on Action Controllers and uses Action Views to implement the template rendering. Action Controllers are then responsible for handling all the actions relating to a certain part of an application. This grouping usually consists of actions for lists and for CRUDs revolving around a single (or a few) model objects. So ContactController would be responsible for listing contacts, creating, deleting, and updating contacts. A WeblogController could be responsible for both posts and comments.

Action View templates are written using embedded Ruby in tags mingled in with the HTML. To avoid cluttering the templates with code, a bunch of helper classes provide common behavior for forms, dates, and strings. And it's easy to add specific helpers to keep the separation as the application evolves.

Note: Some of the features, such as scaffolding and form building, are tied to ActiveRecord (an object-relational mapping package), but that doesn't mean that Action Pack depends on Active Record. Action Pack is an independent package that can be used with any sort of backend (Instiki, which is based on an older version of Action Pack, used Madeleine for example). Read more about the role Action Pack can play when used together with Active Record on

A short rundown of the major features:

  • Actions grouped in controller as methods instead of separate command objects and can therefore share helper methods.

    BlogController < ActionController::Base
      def display
        @customer = find_customer
      def update
        @customer = find_customer
        @customer.attributes = params[:customer] ? 
          redirect_to(:action => "display") : 
          render(:action => "edit")
        def find_customer() Customer.find(params[:id]) end

    Learn more

  • Embedded Ruby for templates (no new “easy” template language)

    <% for post in @posts %>
      Title: <%= post.title %>
    <% end %>
    All post titles: <%= @post.collect{ |p| p.title }.join ", " %>
    <% unless @person.is_client? %>
      Not for clients to see...
    <% end %>

    Learn more

  • Builder-based templates (great for XML content, like RSS)

    xml.rss("version" => "2.0") do do
        xml.description "Basecamp: Recent items"
        xml.language "en-us"
        xml.ttl "40"
        for item in @recent_items
          xml.item do

    Learn more

  • Filters for pre and post processing of the response (as methods, procs, and classes)

    class WeblogController < ActionController::Base
      before_filter :authenticate, :cache, :audit
      after_filter { |c| c.response.body = GZip::compress(c.response.body) }
      after_filter LocalizeFilter
      def list
        # Before this action is run, the user will be authenticated, the cache
        # will be examined to see if a valid copy of the results already
        # exists, and the action will be logged for auditing.
        # After this action has run, the output will first be localized then 
        # compressed to minimize bandwidth usage
        def authenticate
          # Implement the filter with full access to both request and response

    Learn more

  • Helpers for forms, dates, action links, and text

    <%= text_field "post", "title", "size" => 30 %>
    <%= html_date_select( %>
    <%= link_to "New post", :controller => "post", :action => "new" %>
    <%= truncate(post.title, 25) %>

    Learn more

  • Layout sharing for template reuse (think simple version of Struts Tiles)

    class WeblogController < ActionController::Base
      layout "weblog_layout"
      def hello_world
    Layout file (called weblog_layout):
      <html><body><%= @content_for_layout %></body></html>
    Template for hello_world action:
      <h1>Hello world</h1>
    Result of running hello_world action:
      <html><body><h1>Hello world</h1></body></html>

    Learn more

  • Routing makes pretty urls incredibly easy

    map.connect 'clients/:client_name/:project_name/:controller/:action'
    Accessing /clients/37signals/basecamp/project/dash calls ProjectController#dash with
    { "client_name" => "37signals", "project_name" => "basecamp" } in @params["params"]
    From that URL, you can rewrite the redirect in a number of ways:
    redirect_to(:action => "edit") =>
    redirect_to(:client_name => "nextangle", :project_name => "rails") =>

    Learn more

  • Javascript and Ajax integration.

    link_to_function "Greeting", "alert('Hello world!')"
    link_to_remote "Delete this post", :update => "posts", 
                   :url => { :action => "destroy", :id => }

    Learn more

  • Pagination for navigating lists of results.

    # controller
    def list
      @pages, @people =
        paginate :people, :order => 'last_name, first_name'
    # view
    <%= link_to "Previous page", { :page => @pages.current.previous } if @pages.current.previous %>
    <%= link_to "Next page", { :page => } if %>

    Learn more

  • Easy testing of both controller and template result through TestRequest/Response

    class LoginControllerTest < Test::Unit::TestCase
      def setup
        @controller =
        @request    =
        @response   =
      def test_failing_authenticate
        process :authenticate, :user_name => "nop", :password => ""
        assert flash.has_key?(:alert)
        assert_redirected_to :action => "index"

    Learn more

  • Automated benchmarking and integrated logging

    Processing WeblogController#index (for at Fri May 28 00:41:55)
    Parameters: {"action"=>"index", "controller"=>"weblog"}
    Rendering weblog/index (200 OK)
    Completed in 0.029281 (34 reqs/sec)
    If Active Record is used as the model, you'll have the database debugging
    as well:
    Processing WeblogController#create (for at Sat Jun 19 14:04:23)
    Params: {"controller"=>"weblog", "action"=>"create",  
             "post"=>{"title"=>"this is good"} }
    SQL (0.000627) INSERT INTO posts (title) VALUES('this is good')
    Redirected to http://test/weblog/display/5
    Completed in 0.221764 (4 reqs/sec) | DB: 0.059920 (27%)
    You specify a logger through a class method, such as:
    ActionController::Base.logger ="Application Log")
    ActionController::Base.logger ="Application Log")
  • Caching at three levels of granularity (page, action, fragment)

    class WeblogController < ActionController::Base
      caches_page :show
      caches_action :account
      def show
        # the output of the method will be cached as 
        # ActionController::Base.page_cache_directory + "/weblog/show/n.html"
        # and the web server will pick it up without even hitting Rails
        # the output of the method will be cached in the fragment store
        # but Rails is hit to retrieve it, so filters are run
      def update
        List.update(params[:list][:id], params[:list])
        expire_page   :action => "show", :id => params[:list][:id]
        expire_action :action => "account"
        redirect_to   :action => "show", :id => params[:list][:id]

    Learn more

  • Component requests from one controller to another

    class WeblogController < ActionController::Base
      # Performs a method and then lets hello_world output its render
      def delegate_action
        render_component :controller => "greeter",  :action => "hello_world"
    class GreeterController < ActionController::Base
      def hello_world
        render_text "Hello World!"
    The same can be done in a view to do a partial rendering:
      Let's see a greeting:
      <%= render_component :controller => "greeter", :action => "hello_world" %>

    Learn more

  • Powerful debugging mechanism for local requests

    All exceptions raised on actions performed on the request of a local user
    will be presented with a tailored debugging screen that includes exception
    message, stack trace, request parameters, session contents, and the
    half-finished response.

    Learn more

  • Scaffolding for Action Record model objects

    require 'account' # must be an Active Record class
    class AccountController < ActionController::Base
      scaffold :account
    The AccountController now has the full CRUD range of actions and default
    templates: list, show, destroy, new, create, edit, update


  • Form building for Active Record model objects

    The post object has a title (varchar), content (text), and 
    written_on (date)
    <%= form "post" %>
    ...will generate something like (the selects will have more options, of
    <form action="create" method="POST">
        <input type="text" name="post[title]" value="<%= @post.title %>" />
        <textarea name="post[content]"><%= @post.title %></textarea>
        <b>Written on:</b><br/>
        <select name='post[written_on(3i)]'><option>18</option></select>
        <select name='post[written_on(2i)]'><option value='7'>July</option></select>
        <select name='post[written_on(1i)]'><option>2004</option></select>
      <input type="submit" value="Create">
    This form generates a @params["post"] array that can be used directly in a save action:
    class WeblogController < ActionController::Base
      def save
        post = Post.create(params[:post])
        redirect_to :action => "display", :id =>

    Learn more

  • Runs on top of WEBrick, CGI, FCGI, and mod_ruby

Simple example

This example will implement a simple weblog system using inline templates and an Active Record model. So let's build that WeblogController with just a few methods:

require 'action_controller'
require 'post'

class WeblogController < ActionController::Base
  layout "weblog/layout"

  def index
    @posts = Post.find_all

  def display
    @post = Post.find(:params[:id])

  def new
    @post =

  def create
    @post = Post.create(params[:post])
    redirect_to :action => "display", :id =>

WeblogController::Base.template_root = File.dirname(__FILE__)
WeblogController.process_cgi if $0 == __FILE__

The last two lines are responsible for telling ActionController where the template files are located and actually running the controller on a new request from the web-server (like to be Apache).

And the templates look like this:

  <%= @content_for_layout %>

  <% for post in @posts %>
    <p><%= link_to(post.title, :action => "display", :id => %></p>
  <% end %>

    <b><%= post.title %></b><br/>
    <b><%= post.content %></b>

  <%= form "post" %>

This simple setup will list all the posts in the system on the index page, which is called by accessing /weblog/. It uses the form builder for the Active Record model to make the new screen, which in turn hands everything over to the create action (that's the default target for the form builder when given a new model). After creating the post, it'll redirect to the display page using an URL such as /weblog/display/5 (where 5 is the id of the post).


Action Pack ships with three examples that all demonstrate an increasingly detailed view of the possibilities. First is blog_controller that is just a single file for the whole MVC (but still split into separate parts). Second is the debate_controller that uses separate template files and multiple screens. Third is the address_book_controller that uses the layout feature to separate template casing from content.

Please note that you might need to change the “shebang” line to #!/usr/local/env ruby, if your Ruby is not placed in /usr/local/bin/ruby


The latest version of Action Pack can be found at

Documentation can be found at


You can install Action Pack with the following command.

% [sudo] ruby install.rb

from its distribution directory.


Action Pack is released under the MIT license.


The Action Pack homepage is You can find the Action Pack RubyForge page at And as Jim from Rake says:

Feel free to submit commits or feature requests.  If you send a patch,
remember to update the corresponding unit tests.  If fact, I prefer
new feature to be submitted in the form of new unit tests.

For other information, feel free to ask on the ruby-talk mailing list (which is mirrored to comp.lang.ruby) or contact [email protected].